The main process of Earth’s evolution is the cooling of a molten interior, which causes liquid rock to crystallize into solid rock; plate motion is a byproduct of that cooling process, not the primary driver.
Two major settings where Earth materials are produced through plate tectonics:
Mid-ocean ridges: magma solidifies to form basalt, a relatively dense rock.
Subduction zones: magmas form and crystallize to produce continental crust (granite), which is lower density than basalt.
Basalt: a dense, dark, basic rock; granite: a lighter, continental crust rock built largely from lower-density minerals.
Visual cue: granite often has a mix of minerals (pink, black, white, clear) that become visible up close, whereas from a distance it can look nondescript.
Rocks and minerals: definitions and composition
Rocks are aggregates made of minerals; the basic idea is that rocks are composed of smaller units called minerals.
Granitic composition as an example: granite contains multiple minerals that together form the rock.
Core definitions:
A mineral is characterized by a set of properties, often summarized as:
Naturally occurring
Inorganic (not produced by life processes)
Solid
Crystalline (atoms arranged in a repeating 3D pattern)
Fixed chemical composition (or a very narrow range of compositions)
Extra clarifications:
Organic vs inorganic: minerals form without life processes; life-made substances (e.g., wood, leaves) are organic.
Crystallinity means minerals have a consistent, repeating atomic arrangement, which gives rise to definite shapes and cleavage.
Example to illustrate composition: granite contains several minerals (pink, black, white, clear) that together define the rock; different minerals in specific proportions determine the rock’s identity.
Definition of mineral has two key refinements beyond the basics:
Crystalline solid: the atoms are arranged in a highly ordered, repeating pattern in three dimensions.
Consistent composition: the mineral is a specific chemical formula or a constrained set of formulas (e.g., NaCl in halite).
Crystals: forms, patterns, and examples
Minerals are often crystalline; their external shape reflects internal atomic arrangement.
Halite (rock salt) as a canonical example:
Chemical formula: extNaCl
Atoms arranged in a cubic pattern; in halite, sodium ions (Na⁺) and chloride ions (Cl⁻) occupy a regular 3D lattice with a 1:1 ratio: extNa:Cl=1:1
The cubic arrangement is visible at macroscopic scales (halite crystals can be seen as cubes), and at the atomic scale the same packing repeats.
On the tongue, salt dissolves as saliva disrupts the ionic bonds, illustrating how solubility depends on chemical forces.
Other minerals used to illustrate crystal forms:
Pyrite (fool’s gold): iron sulfide with a strong cubic habit and many right angles.
Mica: sheets of crystal structure; bonds within sheets are strong, bonds between sheets are weak, allowing sheets to be peeled apart.
Quartz: often forms well-shaped crystals; important for light transmission and industrial uses.
Gypsum: forms as crystals that can grow into blades; very soft and easily scratched.
Takeaway: the visible shapes of minerals (crystal forms) reflect the underlying atomic arrangement that holds the mineral together.
How minerals form: crystallization and precipitation
Most minerals form by crystallization from liquid rock (magma or lava), depending on location relative to the surface:
Magma cools and minerals crystallize as the melt solidifies.
Minerals can also form by precipitation from solution, not through life processes:
Ions in solution bond and precipitate to form solids.
Visual example: Bonneville Salt Flats, Utah
~30,000 years ago, this area hosted Lake Bonneville; as the climate became more arid, the lake dried up.
Evaporation concentrates dissolved ions; when concentration reaches saturation, minerals such as halite precipitate and form solid deposits.
Direct evidence for an ancient lake environment is provided by these evaporite deposits.
Key takeaway: two primary mineral-formation pathways are crystallization from cooling magma and precipitation from evaporating solutions; life generally does not play a direct role in mineral formation.
Mineral use in society
Minerals are the raw materials for nearly all solid structures in society; much of modern material science is built on mineral resources.
Calcite (calcium carbonate, extCaCO3) is a primary cementing agent in concrete, acting as the binder that glues aggregates together to form a solid mass.
Quartz (silicon dioxide, extSiO2) is crucial for glass production; it lacks weak planes that would otherwise cause breakage or distortion of light when melted and formed into glass.
Historical and current uses of quartz and related minerals: glass manufacturing in Morgantown used quartz sand from local sedimentary rocks.
Iron and steel production relies on iron oxides from minerals like hematite and magnetite; iron is extracted and then alloyed with carbon to make steel.
Gypsum (calcium sulfate dihydrate, ext{CaSO}4 2 ext{H}2 ext{O}) is ground into a powder and used to produce drywall (sheetrock); the gypsum core is sandwiched between paper layers.
Summary: minerals underpin building materials, glass, metals, and many industrial products; society’s demand for mineral-based materials remains high, though plastics are increasingly replacing some applications.
Mining concepts: ore, deposits, and profitability
Ore: a concept rather than a physical object; an ore is any mineral/resource that can be mined and processed profitably.
Profitability is the key criterion for what counts as an ore; even common minerals can be an ore if the economics work.
Geologic maps and mineral associations:
Geologic maps display rock types across landscapes; certain rocks are statistically associated with specific ores, guiding exploration.
Concentration and ore quality:
Determining ore concentration (how much of the target mineral is present) is essential to assess profitability; high concentration makes mining more viable.
The mining ratio (conceptual and practical):
The mining ratio is a visual/quantitative way to assess the cost of extraction relative to ore content.
Definition (conceptual):
Let overburden be the rock/soil above the ore deposit; the ore volume is the target; the mining ratio is the comparison of these volumes:
ext{Mining ratio} = rac{V{ ext{overburden}}}{V{ ext{ore}}}
Interpretation:
A low mining ratio (little overburden relative to ore) is generally favorable for profitability; a high ratio means more material must be moved, increasing costs.
Open-pit mining considerations and an illustrative case: Berkeley Pit, Butte, Montana
Berkeley Pit opened in 1955 and operated until 1982; it targeted copper and other metals.
Total material moved: 1,500,000,000 tons (mostly tailings), with comparatively small copper extraction.
The pit exposes zones around ancient magma chambers, where hot water driven by magma circulated through surrounding rocks.
These circulating fluids caused precipitation of metal-bearing minerals around the magma chamber (the purple halos in 3D models).
After mining ceased, the pit filled with water; contact with remaining ore led to weathering and redox reactions that released metals into solution.
The water’s color change and acidity were due to sulfide minerals reacting with air and water to form sulfate minerals such as extH<em>2extSO</em>4, sulfuric acid, which lowered pH to about pH≈ext2.5, harming aquatic life (acidic, metal-rich lake).
This created a positive feedback loop: more acidic water leaches more metals, sustaining the toxic environment.
A key environmental lesson: abandoned mines can become severe pollution problems if not properly managed.
Recovery and new opportunities:
The pit’s water level has been kept in check by pumping and treating water to remove dissolved metals.
The process can recover not only common metals but also rare earth elements (REEs), which are critical for high-tech applications and defense.
The U.S. Department of Defense has funded WVU to study water treatment for potential extraction of REEs from Berkeley Pit water and similar mine waters.
Rare earth elements (REEs) and critical minerals
REEs are essential for modern technologies: smartphones, laptops, EVs, magnets in wind turbines, etc.
They are typically found as oxides and are widely dispersed in rocks rather than in high-concentration veins, making extraction from ore impractical in many cases.
Extracting REEs from aqueous solutions (e.g., pumped mine waters) could provide an alternative, potentially domestic source and reduce reliance on foreign supply chains.
Terminology and scope:
The orange-colored elements in references to REEs are illustrative; the exact list is not required to memorize, but they are typically trivalent or other oxidation states and often occur as oxides.
The critical/mineral supply context emphasizes the strategic importance of securing stable REE sources for technology and defense.
Practical and ethical implications
Environmental stewardship: mining and mine water treatment must consider ecological impacts, downstream water quality, and long-term sustainability.
Economic balance: mining decisions hinge on ore concentration, access costs (overburden), market prices, and regulatory/social considerations.
Geopolitical considerations: reliance on external suppliers for critical minerals can influence national security and economic resilience; domestic extraction and processing are increasingly pursued.
Innovation opportunities: treating mine waters to recover REEs represents an intersection of geology, chemistry, engineering, and policy, with potential societal benefits.
Connections to broader geology and real-world relevance
Mineral basics connect directly to geology as the building blocks of rocks and landforms, linking microscopic crystal structure to macroscopic rock properties.
The study of minerals informs resource exploration, materials science, construction, and manufacturing.
Understanding environmental impacts of mining highlights the need for sustainable practices, remediation, and new resource pipelines (e.g., water-based recovery methods for critical minerals).
The Berkeley Pit case demonstrates how geological processes, engineering projects, and environmental policy intersect in real-world settings and can transform from a disposal issue into a resource opportunity.
The discussion of rare earth elements underscores the importance of supply chain resilience for modern technology and national security, illustrating how geology translates into strategic considerations.
Key terms and formulas to remember
Mineral definitions and criteria:
Naturally occurring, extinorganic, solid, crystalline with a definite chemical composition
Crystal structure concepts:
Halite crystal:
extNaCl with a 1:1 ratio: extNa:Cl=1:1
Crystalline solids have a repeating 3D structure; crystal faces reflect atomic arrangement.
Formation processes:
Crystallization from magma: solidification of molten rock.
Precipitation from solution: formation of solids from dissolved ions.
Evaporite example:
Evaporation drives precipitation of minerals like halite in drying lakes (e.g., Bonneville Salt Flats).
Lower ratio generally favors profitability; higher ratio increases extraction costs.
Notable chemical species:
Carbonates and silicates: extCaCO<em>3,extSiO</em>2
Gypsum: ext{CaSO}4 2 ext{H}2 ext{O}
Sulfuric acid: extH<em>2extSO</em>4
Time scales and quantities:
~30,000 years ago for Bonneville Lake evaporation context: t≈3imes104extyearsago
Berkeley Pit material moved: 1,500,000,000exttons (mostly tailings)
Opened: 1955; closed: 1982
Significance of REEs:
Critical minerals essential for magnets and tech; often exist as oxides; distribution is broad but concentrations are low, making extraction challenging.